1. Field of the Invention
The present invention relates to a nail that is used, for example, to join lumber and the like.
2. Description of the Related Art
Related art includes Japanese Patent Laid-open Publication No. 2004-32912 and Japanese Patent Laid-open Publication No. 2003-97523.
Since the past, nails have been made of soft iron materials. A head portion is formed in an upper end portion of a columnar body. A circular conical or pyramidal tip end portion is formed in a lower end portion.
A nail that is formed in this manner can be smoothly driven into a piece of lumber in a section that has no knots, with the circular conical or pyramidal tip end portion. However, the nail has a disadvantage in that when the tip end portion hits a knotty portion, the nail is driven in a bent manner.
To solve this disadvantage, a following drive nail is considered. A lower end of the drive nail is formed into the shape of an inverted cone. A lower end of the inverted cone forms a planar tip end surface that is orthogonal to an axial line. A recessing cavity is formed in the center of the planar tip end surface such as to recess upward. A recessing groove wall is thereby maintained in the overall periphery of the recessing cavity. The drive nail meets the Japanese Industrial Standards. However, when this drive nail is used, there is a disadvantage in that, when the tip end portion hits a knot, the recessing groove wall in the overall periphery of the recessing cavity easily collapses because the drive nail is composed of a soft iron material to meet the Japanese Industrial Standards. The nail is driven in a bent manner. In addition, there is also a disadvantage in that work involved in forming the recessing groove wall in the overall periphery of the recessing cavity is painstaking and cost increases.